Plant scientists have recognized for many years that the hybridization of closely related plants may result in the production of offspring having a combination of desirable traits which previously were possessed separately by the parent plants. Also, hybrid plants of various crops commonly have possessed a vigor or heterosis which has contributed significantly to the crop yield and accordingly has been of considerable economic importance.
Since the plants selected for hybridization studies commonly are capable of undergoing both self-pollination and cross-pollination, the desired crossing often has been difficult to achieve on a reliable basis while operating on a commercially viable scale. Accordingly, controlled cross-pollination must be achieved in the substantial absence of self-pollination. A common technique heretofore utilized to accomplish this goal has been the use of cytoplasmic male sterile plants as the seed parent which are grown as a substantially uniform population adjacent to another substantially uniform population of plants from which the pollen is derived. Such technique has required precise control of the planting patterns, sufficient pollen transfer from one block of plants to another, and precise control of the seed harvest to preclude comingling of the two different seed products which are produced.
In U.S. Pat. No. 3,842,538 is disclosed a method of hybrid seed grain production wherein the bulk planting of cytoplasmic male sterile parent and the pollen parent is proposed. The seeds capable of forming hybrid plants are thereafter separated from the non-hybrid seeds on the basis of color. Such seed separation technique still would be tedious; however, and is not believed to have been commercially adopted. Articles by D. E. Falk, K. J. Kasha, and E. Reinbergs appearing in Proceedings of the Fourth International Barley Genetics Symposium, July 22 to 29, 1981, (Edinburgh University Press), pages 778 to 785, and by D. E. Falk and K. J. Kasha appearing in Crop Science, Vol. 22, March-April, 1982, page 450, discuss a tight linkage between genetic male sterility and a shrunken endosperm. See also, U.S. Pat. No. 4,351,130 which discloses a process for cereal production wherein tall male parents and short female parents can be grown in the same planting area, and after pollination the male parents are destroyed.
While considerable success has been realized in the past through the adoption of various well-known hybridization techniques, the need nevertheless has remained for alternate, less tedious, more efficient, or otherwise improved hybridization routes. Additionally, for many crops commercially feasible hybridization technology is yet to be implemented in spite of continuing research by dedicated plant scientists working around the world.
An example of a crop which is yet to benefit from the commercial availability of seed capable of growing hybrid plants is rape (i.e., Brassica napus or Brassica campestris). While not necessarily recognized by the general public, rape (and particularly high-quality forms thereof known as canola) is being grown as an increasingly important oilseed crop and a source of rape-seed meal in many parts of the world. The oil may serve as a high-quality vegetable oil and the meal may be used as a nutritious protein concentrate for livestock. The importance of rape as an agronomic crop is discussed in (1) Highlights of Agricultural Research in Ontario, December 1982, at pages 18-19 in an article by W. D. Beversdorf and David J. Hume, entitled "Canola: A New Oilseed Crop for Ontario," and in (2) The Ontario Ministry of Agriculture and Food Factsheet No. 82-017, February 1982, entitled, "Spring Canola in Ontario" by D. J. Hume, R. J. McLaughlin and W. D. Beversdorf.
Representative publications of researchers working in the area of rapeseed technology who have identified cytoplasmic male sterility in rape plants are identified below:
Bannerot, H., Boulidard, I., Cauderon, Y., and Tempe, J., "Cytoplasmic Male Sterility Transfer From Raphanus to Brassica," Proc. Eucarpia Meeting Cruciferae Vegetable Crop, Sect. 25:52-54 (1974).
Bartkowiak-Broda, I., Rousselle, P., and Renard, M., "Investigation of Two Kinds of Cytoplasmic Male Sterility in Rape (Brassica napus L.)," Genet. Polon. 20:487-497 (1979).
Ohkawa, Y., Shiga, T., and Ishige, T., "Male Sterility-Inducing-Cytoplasm in Brassica campestris var. rapifera, Annual Report, Division of Genetics, Dept. of Physiol. and Genetics, Nat. Inst. of Agric. Sciences, Kannondai, Yatabe, Tsukuba, Japan, pp. 30-31 (1979).
Palmer, J. D., Shields, C. R., Cohen, D. B., and Orton, T. J., "An Unusual Mitochondrial DNA Plasmid in the Genus Brassica," Nature 301:725-728 (1983).
Rousselle, P., and Renard, M., "Interet du cultivar &lt;&lt;Bronowski&gt;&gt; pour l'obtention de plantes male-steriles cytoplasmiques chez le colza (Brassica napus L.)," Agronomie 2 (10):951-956 (1982).
Shiga, T., "Studies on Heterosis Breeding Using Cytoplasmic Male Sterility in Rapeseed., Brassica napus L.", Bull. Nat. Inst. Agric. Sci., Tokyo Series D. 27:75-85 (1976).
Shiga, T., "Cytoplasmic Male Sterility and Its Utilization for Heterosis Breeding in Rapeseed (Brassica napus L.)", JARQ 10:177-182 (1976).
Shiga, T., "Male Sterility and Cytoplasmic Differentiation," Chapter 12 in Brassica Crops and Wild Allies-Biology and Breeding, Japan Sci. Soc. Press, Tokyo, pp. 205-221 (1980).
Thompson, K. F., "Cytoplasmic Male-Sterility in Oil-Seed Rape," Heredity 29(2):253-257 (1972).
Vedel, F., Mathieu, C., Lebacq, P., Ambard-Bretteville, F., and Remy, R., "Comparative Macromolecular Analysis of the Cytoplasms of Normal and Cytoplasmic Male Sterile Brassica napus," Theor. Appl. Genet. 62:255-262 (1982).
It has also been recognized in the past that weed control is an important consideration for those who choose to grow rape. Unchecked weeds will lessen the ultimate yield and can significantly reduce the quality by unavoidable contamination from diverse seeds which are harvested along with the desired crop. In order to deal with the weed problem various herbicide tolerant varieties of rape have been proposed so that unwanted weeds can be efficiently eliminated while growing in close proximity to the rape plants. See in this regard, "Transfer of Cytoplasmically-Inherited Triazine Resistance From Bird's Rape to Cultivated Oilseed Rape (Brassica campestris and B. napus)," by W. D. Beversdorf, J. Weiss-Lerman, L. R. Erickson and V. Souza Machado appearing in the Canadian Journal of Genetics and Cytology, Volume XXII, No. 2, June 1980, pages 167-172. See also "Uniparental Inheritance of Chloroplast Atrazine Tolerance in Brassica Campestris" by V. Souza Machado, J. D. Bandeen, G. R. Stephenson and P. Lavigne, Can. J. Plant Sci., 58:977-981, 1978.
In our U.S. Pat. No. 4,517,763 entitled, "Hybridization Process Utilizing a Combination of Cytoplasmic Male Sterility and Herbicide Tolerance" is disclosed a hybridization process in which the bulk planting of the parents is made possible. This disclosure additionally was published as U.K. Patent Application GB No. 2,139,466A on Nov. 14, 1984.
It additionally has been recognized that plants can be identified by plant scientists which exhibit herbicide tolerance which is attributable soley to nuclear genes. See, for instance the following representative publications in this area:
Rogers, S. G., Braud, L. A., Holder, S. B., Sharps, E. S. and Brackin, M. J., "Amplification of the aroA Gene from Escherichia Coli Results in Tolerance to Herbicide Glyphosate", Applied and Environmental Microbiology, 46 (1):37-43 (1983).
Chaleff, R. S. and Ray, T. B., "Herbicide-Resistant Mutants from Tobacco Cell Cultures", Science, 223:1147-1150 (1984).
Singer, S. R. and McDaniel, C. N., "Selection of Amitrole Tolerant Tobacco Calli and the Expression of this Tolerance in Regenerated Plants and Progeny", Theor. Appl. Genet., 67:427-432 (1984).
Singer, S. R. and McDaniel, C. N., "Selection of Glyphosate-Tolerant Tobacco Calli and the Expression of this Tolerance in Regenerated Plants", Plant Physiol. 78:411-416 (1985).
Comai, L., U.S. Pat. No. 4,535,060, "Inhibition Resistant 5-Enolpyruvyl-3-Phosphoshickimate Synthetase, Production and Use" (1985).
See also our copending U.S. Ser. No. 797,916, filed concurrently herewith, entitled, "Hybridization Process Utilizing a Combination of Cytoplasmic Male Sterility, Cytoplasmic Herbicide Tolerance, and Herbicide Tolerance Attributable Solely to Nuclear Genes".
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination wherein the seed parent is cytoplasmic male sterile and wherein the pollen parent conveniently may be grown in bulk with the seed parent during a step of the process without the need for a precise planting pattern and the disadvantages associated therewith.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop wherein the cross-fertilization of cytoplasmic male sterile plants with maintainer plants readily may be accomplished.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination wherein the desired product may be formed on a reliable basis.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination which is suitable for utilization on an economical basis on a commercially attractive scale.
It is an object of the present invention to provide an improved hybridization process for use in forming a predetermined hybrid variety of a crop which is capable of undergoing both self-pollination and cross-pollination wherein the desired product in a preferred embodiment additionally exhibits herbicide tolerance which makes possible the selective destruction with ease of troublesome weeds growing within the hybrid crop area.
It is an object of the present invention to provide an improved hybridization process which particularly is suited for use when forming a predetermined hybrid variety of rape (e.g., Brassica napus), and to thereby provide a commercially practicable route for forming hybrid rape.
It is another object of the present invention to provide a new and useful Brassica napus seed product which is suitable for use when carrying out the process of the present invention.
It is a further object of the present invention to provide a Brassica napus seed product which is capable of forming F.sub.1 hybrid rape plants which exhibit tolerance to at least one herbicide attributable solely to nuclear genes.
These and other objects and advantages will be apparent to those skilled in the art from reading of the following description and appended claims.